In a conventional steering control apparatus disclosed in JP-A-2000-238654, a steering reaction torque is determined by the following.steering reaction torque=K·tire reaction torque+correction valueWhere, the correction value is set from a vehicle speed and a steering angle.
By this, a steering reaction torque characteristic (steering angle—steering reaction torque characteristic) with a suitable hysteresis is realized.
Besides, in a convention steering control apparatus disclosed in JP-A-2002-274405, a steering reaction torque is determined by the following. By that, in a separate type power steering apparatus in which mechanical coupling is not performed, a steering feeling comparable to that of a vehicle equipped with a conventional power steering apparatus is realized.steering reaction torque The=(1+f(o))−1SAT                SAT: Self Aligning Torque        f(o): assist torque Tem=f(o) The        
Besides, in a conventional steering control apparatus disclosed in JP-A-2002-19631, a steering reaction torque with a hysteresis is generated by a turning increase/turning back judgment means and a previously set relational expression between a steering wheel angle and a steering reaction torque.
In the conventional steering control apparatus disclosed in JP-A-2000-238654, although the hysteresis and the slope of the steering reaction torque can be adjusted by ┌steering reaction torque=K·tire reaction torque+correction value┘, it is necessary to previously set the correction value, and there is a case where a suitable correction value is not obtained according to a change in road surface friction μ or the like.
Further, in the conventional steer-by-wire disclosed in JP-A-2002-274405, since the steering reaction torque is set from the relation of the assist map of the power steering and the estimated self-aligning torque, the steering feeling comparable to the vehicle equipped with the power steering system can be obtained, however, it is not easy to freely set the hysteresis width and the slope of the steering reaction torque so as to improve the steering feeling more than the vehicle equipped with the conventional power steering apparatus.
Besides, in the conventional steering control apparatus disclosed in JP-A-2002-19631, since it is necessary to previously set the relational expression between the steering wheel angle and the steering reaction torque, in order to set a complicated steering reaction torque, the number of matching steps is increased, and the computation processing becomes complicated. Further, an external force exerted on a wheel is changed by a road surface friction coefficient, a steering state, and the like. According to the steering reaction torque mathematically obtained from the steering angle and the vehicle speed, it is impossible to perform a control to obtain a steering reaction torque in which the external force exerted on the wheel and friction inherent in the steering apparatus are sufficiently taken into consideration, and therefore, there is a problem that the behavior of a vehicle can not be recognized, and there is a, fear that the steering feeling is degraded.